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Understanding Efficiency. Human Circuit. How does it work?. Remember how lie detectors work? People are conductors. Electricity is nothing more than free electrons moving from atom to atom through a material. This flow is called a current .

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Understanding Efficiency


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Presentation Transcript
how does it work
How does it work?
  • Remember how lie detectors work? People are conductors.
  • Electricity is nothing more than free electrons moving from atom to atom through a material. This flow is called a current.
  • Since your body is mostly water and there are water and minerals on your skin, your body can be a conductor, but it’s not a great one.
some motors run on direct current
Some motors run on direct current:
  • Electricity runs in one directions.
  • Mp3 players, computers, cell phones & calculators also use DC.
  • Plug-in devices that run on DC come with their own power supplies that convert the power company’s 120-V AC to DC.
the electricity in household circuits is ac
The Electricity in household circuits is AC
  • “Alternating Current” flows back and forth, 60 times per second.
why do power companies generate ac
Why do power companies generate AC?
  • With AC they can use transformers.
  • Transformers change the amount of voltage with hardly any energy loss.
  • Changing voltage is necessary because the most efficient way to transmit current over long distances is at a high voltage.
slide7
But…
  • When transmission lines carry current at 500 000 V, the voltage must be reduced before it can be used in your home.
generating electricity
Generating Electricity
  • Remember our good friend Michael Faraday?
electromagnetic induction
Electromagnetic Induction
  • Faraday demonstrated that electrical current could be generated (by moving a conducting wire through a magnetic field).
  • This changed the world because it introduced a way to generate a steady supply of large amounts of electricity.
  • Generators coils of wire that are moved through a magnetic field.
tokyo s toshima incineration plant
Tokyo's Toshima Incineration Plant
  • Burns 300 tons of garbage a day, turning it into electricity, hot water and a kind of recyclable sand.
the unit of power is
The unit of power is:
  • The Watt (W) – Named for James Watt
  • A watt is equal to one joule per second.
  • The faster a device converts energy, the greater its power rating.
power ratings
Power Ratings:
  • Most small appliances: 1500 W or less
  • Stove: 7000 W
  • Calculator: 0.4 mW
mathematically
Mathematically:
  • Power is equal to the current multiplied by the voltage.
  • Power (P); current (I); voltage (V)
energy measured in joules watts x seconds
Energy: Measured in Joules (watts x seconds)
  • You can use the power rating of a device to figure out the amount of energy the device uses.
  • Remember that power is the rate at which a device converts energy. You can find the amount of energy by multiplying this rate by the length of time the device operates.
kilowatt hours
Kilowatt Hours
  • People use a lot of joules of energy in their homes/businesses, so kilowatt hours are often used as a unit for energy.
  • Calculation is the same, except hours are substituted for seconds, and kilowatts (kW) are substituted for watts.
  • Electricity meters measure the energy used in kilowatt hours.
law of conservation of energy
Law of Conservation of Energy
  • Energy cannot be created or destroyed.
  • It does not just appear or disappear… it must be transformed from one form to another.
read page 335 342
Read: Page 335-342
  • Check & Reflect, page 342, #1-7